Magnetocardiography: ventricular arrhythmias

Since 1985, magnetocardiographic (MCG) mapping has been carried out in patients with severe ventricular arrhythmias, related to primary cardiomyopathy and ischaemic heart disease, for the purpose of non-invasive localization of the arrhythmogenic substrate or to screen patients at risk of sudden death. Data reported by several authors have demonstrated that magnetocardiography is useful to investigate non-invasively some of the possible electrogenetic abnormalities underlying clinical arrhythmias and to identify patients at risk of sudden death through the detection of late magnetic fields and quantitative estimation of repolarization/depolarization abnormalities. In this paper all the above-mentioned applications have been briefly reviewed. Experience based on 35 patients, with Lown class 3 or higher ventricular arrhythmias, who have been studied magnetically, to localize the site of origin of their ventricular arrhythmia and to calculate their Relative Smoothness Index is described. Reproducible MCG three-dimensional localization of both ventricular extrasystoles and sustained tachycardia proved possible, using even single channel instrumentation, with an accuracy in the order of 10 mm as demonstrated by inverse localization of a biomagnetic catheter. The RS index was significantly lower in patients with cardiomyopathy or sudden death, but this parameter needs further investigation, as methodological drawbacks could impair its clinical reliability. In conclusion, MCG localization of the arrhythmogenic substrate can be useful to guide aimed invasive electrophysiology, biopsy and ablation close to-the arrhythmogenic substrate.